/* Copyright (c) 2005-2018 Dovecot authors, see the included COPYING file */

#include "common.h"
#include "array.h"
#include "ioloop.h"
#include "hash.h"
#include "llist.h"
#include "str.h"
#include "safe-mkstemp.h"
#include "time-util.h"
#include "sleep.h"
#include "master-client.h"
#include "service.h"
#include "service-process.h"
#include "service-process-notify.h"
#include "service-anvil.h"
#include "service-log.h"
#include "service-monitor.h"

#include <unistd.h>
#include <sys/wait.h>
#include <syslog.h>
#include <signal.h>

#define SERVICE_DROP_WARN_INTERVAL_SECS 1
#define SERVICE_DROP_TIMEOUT_MSECS (10*1000)
#define SERVICE_LOG_DROP_WARNING_DELAY_MSECS 500
#define MAX_DIE_WAIT_MSECS 5000
#define SERVICE_MAX_EXIT_FAILURES_IN_SEC 10
#define SERVICE_MIN_SUCCESSFUL_AGE_SECS 10
#define SERVICE_PREFORK_MAX_AT_ONCE 10

static void service_monitor_start_extra_avail(struct service *service);
static void service_status_more(struct service_process *process,
				const struct master_status *status);
static void service_monitor_listen_start_force(struct service *service);

static void service_process_idle_kill_timeout(struct service_process *process)
{
	struct master_status status;

	e_error(process->service->event, "Process %s is ignoring idle SIGINT",
		dec2str(process->pid));

	timeout_remove(&process->to_idle_kill);

	/* assume this process is busy */
	i_zero(&status);
	service_status_more(process, &status);
	process->available_count = 0;
}

static void service_kill_idle(struct service *service)
{
	/* Kill extra idling processes to reduce their number. The idea here is
	   that if the load stays the same, by killing the lowwater number of
	   processes there won't be any extra idling processes left. */
	unsigned int processes_to_kill =
		service->process_idling_lowwater_since_kills;
	service->process_idling_lowwater_since_kills = service->process_idling;

	/* Always try to leave process_min_avail processes */
	i_assert(processes_to_kill <= service->process_avail);
	if (processes_to_kill <= service->set->process_min_avail) {
		if (service->process_idling == 0)
			timeout_remove(&service->to_idle);
		return;
	}
	processes_to_kill -= service->set->process_min_avail;

	/* Now, kill the processes with the oldest idle_start time.

	   (It's actually not important which processes get killed. A better
	   way could be to kill the oldest processes since they might have to
	   be restarted anyway soon due to reaching restart_request_count, but
	   we'd have to use priority queue for tracking that, which is more
	   expensive and probably not worth it.) */
	for (; processes_to_kill > 0; processes_to_kill--) {
		struct service_process *process = service->idle_processes_head;

		i_assert(process != NULL);
		if (process->to_idle_kill != NULL) {
			/* already tried to kill all the idle processes */
			break;
		}

		i_assert(process->available_count == service->client_limit);
		if (kill(process->pid, SIGINT) < 0 && errno != ESRCH) {
			e_error(service->event, "kill(%s, SIGINT) failed: %m",
				dec2str(process->pid));
		}
		process->last_kill_sent = ioloop_time;
		process->to_idle_kill =
			timeout_add(service->idle_kill_interval * 1000,
				    service_process_idle_kill_timeout, process);

		/* Move it to the end of the list, so it's not tried to be
		   killed again. */
		DLLIST2_REMOVE(&service->idle_processes_head,
			       &service->idle_processes_tail, process);
		DLLIST2_APPEND(&service->idle_processes_head,
			       &service->idle_processes_tail, process);
	}
}

static void service_status_more(struct service_process *process,
				const struct master_status *status)
{
	struct service *service = process->service;

	if (process->idle_start != 0) {
		/* idling process became busy */
		DLLIST2_REMOVE(&service->idle_processes_head,
			       &service->idle_processes_tail, process);
		DLLIST_PREPEND(&service->busy_processes, process);
		process->idle_start = 0;

		i_assert(service->process_idling > 0);
		i_assert(service->process_idling <= service->process_avail);
		service->process_idling--;
		service->process_idling_lowwater_since_kills =
			I_MIN(service->process_idling_lowwater_since_kills,
			      service->process_idling);
	}
	process->total_count +=
		process->available_count - status->available_count;

	if (status->available_count != 0)
		return;

	/* process used up all of its clients */
	i_assert(service->process_avail > 0);
	service->process_avail--;
	i_assert(service->process_idling <= service->process_avail);

	if (service->type == SERVICE_TYPE_LOGIN &&
	    service->process_avail == 0 &&
	    service->process_count == service->process_limit)
		service_login_notify(service, TRUE);

	/* we may need to start more */
	service_monitor_start_extra_avail(service);
	service_monitor_listen_start(service);
}

static void service_check_idle(struct service_process *process)
{
	struct service *service = process->service;

	if (process->available_count != service->client_limit)
		return;

	if (process->idle_start == 0) {
		/* busy process started idling */
		DLLIST_REMOVE(&service->busy_processes, process);
		service->process_idling++;
		i_assert(service->process_idling <= service->process_avail);
	} else {
		/* Idling process updated its status again to be idling. Maybe
		   it was busy for a little bit? Update its idle_start time. */
		DLLIST2_REMOVE(&service->idle_processes_head,
			       &service->idle_processes_tail, process);
	}
	DLLIST2_APPEND(&service->idle_processes_head,
		       &service->idle_processes_tail, process);
	process->idle_start = ioloop_time;

	if (service->process_avail > service->set->process_min_avail &&
	    service->to_idle == NULL &&
	    service->idle_kill_interval != UINT_MAX) {
		/* We have more processes than we really need. Start a timer
		   to trigger idle_kill_interval. */
		service->to_idle =
			timeout_add(service->idle_kill_interval * 1000,
				    service_kill_idle, service);
	}
}

static void service_status_less(struct service_process *process)
{
	struct service *service = process->service;

	/* some process got more connections - remove the delayed warning */
	timeout_remove(&service->to_drop_warning);

	if (process->available_count == 0) {
		/* process can accept more clients again */
		if (service->process_avail++ == 0)
			service_monitor_listen_stop(service);
		i_assert(service->process_avail <= service->process_count);
	}
	if (service->type == SERVICE_TYPE_LOGIN)
		service_login_notify(service, FALSE);
}

static void
service_status_input_one(struct service *service,
			 const struct master_status *status)
{
        struct service_process *process;

	process = hash_table_lookup(service_pids, POINTER_CAST(status->pid));
	if (process == NULL) {
		/* we've probably wait()ed it away already. ignore */
		return;
	}

	if (process->uid != status->uid || process->service != service) {
		/* a) Process was closed and another process was created with
		   the same PID, but we're still receiving status update from
		   the old process.

		   b) Some process is trying to corrupt our internal state by
		   trying to pretend to be someone else. We could use stronger
		   randomness here, but the worst they can do is DoS and there
		   are already more serious problems if someone is able to do
		   this.. */
		e_error(service->event, "Ignoring invalid update from child %s "
			      "(UID=%u)", dec2str(status->pid), status->uid);
		return;
	}
	process->last_status_update = ioloop_time;
	/* process worked a bit - it may have ignored idle-kill signal */
	timeout_remove(&process->to_idle_kill);

	/* first status notification */
	timeout_remove(&process->to_status);

	if (process->available_count != status->available_count) {
		if (process->available_count > status->available_count) {
			/* process started servicing some more clients */
			service_status_more(process, status);
		} else {
			/* process finished servicing some clients */
			service_status_less(process);
		}
		process->available_count = status->available_count;
	}
	service_check_idle(process);
}

static void service_status_input(struct service *service)
{
	struct master_status status[1024/sizeof(struct master_status)];
	unsigned int i, count;
	ssize_t ret;

	ret = read(service->status_fd[0], &status, sizeof(status));
	if (ret <= 0) {
		if (ret == 0)
			e_error(service->event, "read(status) failed: EOF");
		else if (errno != EAGAIN)
			e_error(service->event, "read(status) failed: %m");
		else
			return;
		service_monitor_stop(service);
		return;
	}

	if ((ret % sizeof(struct master_status)) != 0) {
		e_error(service->event, "service sent partial status update "
			      "(%d bytes)", (int)ret);
		return;
	}

	count = ret / sizeof(struct master_status);
	for (i = 0; i < count; i++)
		service_status_input_one(service, &status[i]);
	/* If ret==sizeof(status) there may be more input available, but do it
	   in the next ioloop run. This way a single service can't flood the
	   master process and cause it to hang entirely. */
}

static void service_log_drop_warning(struct service *service)
{
	const char *limit_name;
	unsigned int limit;

	if (service->last_drop_warning +
	    SERVICE_DROP_WARN_INTERVAL_SECS <= ioloop_time) {
		service->last_drop_warning = ioloop_time;
		if (service->process_limit > 1) {
			limit_name = "process_limit";
			limit = service->process_limit;
		} else if (service->set->restart_request_count == 1) {
			i_assert(service->client_limit == 1);
			limit_name = "client_limit/restart_request_count";
			limit = 1;
		} else {
			limit_name = "client_limit";
			limit = service->client_limit;
		}
		e_warning(service->event,
			  "%s (%u) reached, client connections are being dropped",
			  limit_name, limit);
	}
}

static void service_monitor_throttle(struct service *service)
{
	if (service->to_throttle != NULL || service->list->destroying)
		return;

	i_assert(service->throttle_msecs > 0);

	e_error(service->event,
		      "command startup failed, throttling for %u.%03u secs",
		      service->throttle_msecs / 1000,
		      service->throttle_msecs % 1000);
	service_throttle(service, service->throttle_msecs);
	service->throttle_msecs *= 2;
	if (service->throttle_msecs >
	    SERVICE_STARTUP_FAILURE_THROTTLE_MAX_MSECS) {
		service->throttle_msecs =
			SERVICE_STARTUP_FAILURE_THROTTLE_MAX_MSECS;
	}
}

static void service_drop_timeout(struct service *service)
{
	struct service_listener *lp;
	int fd;

	i_assert(service->process_avail == 0);

	/* drop all pending connections */
	array_foreach_elem(&service->listeners, lp) {
		while ((fd = net_accept(lp->fd, NULL, NULL)) > 0)
			net_disconnect(fd);
	}

	service_monitor_listen_start_force(service);
	service->listen_pending = TRUE;
}

static void service_monitor_listen_pending(struct service *service)
{
	i_assert(service->process_avail == 0);

	service_monitor_listen_stop(service);
	service->listen_pending = TRUE;

	service->to_drop = timeout_add(SERVICE_DROP_TIMEOUT_MSECS,
				       service_drop_timeout, service);
}

static void service_drop_connections(struct service_listener *l)
{
	struct service *service = l->service;
	int fd;

	if (service->type != SERVICE_TYPE_WORKER)
		service_log_drop_warning(service);

	if (service->type == SERVICE_TYPE_LOGIN) {
		/* reached process limit, notify processes that they
		   need to start killing existing connections if they
		   reach connection limit */
		service_login_notify(service, TRUE);

		service_monitor_listen_pending(service);
	} else if (!service->listen_pending) {
		/* maybe this is a temporary peak, stop for a while and
		   see if it goes away */
		service_monitor_listen_pending(service);
		if (service->to_drop_warning == NULL &&
		    service->type == SERVICE_TYPE_WORKER) {
			service->to_drop_warning =
				timeout_add_short(SERVICE_LOG_DROP_WARNING_DELAY_MSECS,
						  service_log_drop_warning, service);
		}
	} else {
		/* this has been happening for a while now. just accept and
		   close the connection, so it's clear that this is happening
		   because of the limit, rather than because the service
		   processes aren't answering fast enough */
		fd = net_accept(l->fd, NULL, NULL);
		if (fd > 0)
			net_disconnect(fd);
	}
}

static void service_accept(struct service_listener *l)
{
	struct service *service = l->service;

	i_assert(service->process_avail == 0);

	if (service->process_count == service->process_limit) {
		/* we've reached our limits, new clients will have to
		   wait until there are more processes available */
		service_drop_connections(l);
		return;
	}

	/* create a child process and let it accept() this connection */
	if (service_process_create(service) == NULL)
		service_monitor_throttle(service);
	else
		service_monitor_listen_stop(service);
}

static bool
service_monitor_start_count(struct service *service, unsigned int limit)
{
	unsigned int i, count;

	i_assert(service->set->process_min_avail >= service->process_avail);

	count = service->set->process_min_avail - service->process_avail;
	if (service->process_count + count > service->process_limit)
		count = service->process_limit - service->process_count;
	if (count > limit)
		count = limit;

	for (i = 0; i < count; i++) {
		if (service_process_create(service) == NULL) {
			service_monitor_throttle(service);
			break;
		}
	}
	if (i > 0) {
		/* we created some processes, they'll do the listening now */
		service_monitor_listen_stop(service);
	}
	return i >= limit;
}

static void service_monitor_prefork_timeout(struct service *service)
{
	/* don't prefork more processes if other more important processes had
	   been forked while we were waiting for this timeout (= master seems
	   busy) */
	if (service->list->fork_counter != service->prefork_counter) {
		service->prefork_counter = service->list->fork_counter;
		return;
	}
	if (service->process_avail < service->set->process_min_avail) {
		if (service_monitor_start_count(service, SERVICE_PREFORK_MAX_AT_ONCE) &&
		    service->process_avail < service->set->process_min_avail) {
			/* All SERVICE_PREFORK_MAX_AT_ONCE were created, but
			   it still wasn't enough. Launch more in the next
			   timeout. */
			return;
		}
	}
	timeout_remove(&service->to_prefork);
}

static void service_monitor_start_extra_avail(struct service *service)
{
	if (service->process_avail >= service->set->process_min_avail ||
	    service->process_count >= service->process_limit ||
	    service->list->destroying)
		return;

	if (service->process_avail == 0) {
		/* quickly start one process now */
		if (!service_monitor_start_count(service, 1))
			return;
		if (service->process_avail >= service->set->process_min_avail)
			return;
	}
	if (service->to_prefork == NULL) {
		/* ioloop handles timeouts before fds (= SIGCHLD callback),
		   so let the first timeout handler call simply update the fork
		   counter and the second one check if we're busy or not. */
		service->to_prefork =
			timeout_add_short(0, service_monitor_prefork_timeout, service);
	}
}

static void service_monitor_listen_start_force(struct service *service)
{
	struct service_listener *l;

	service->listening = TRUE;
	service->listen_pending = FALSE;
	timeout_remove(&service->to_drop);
	timeout_remove(&service->to_drop_warning);

	array_foreach_elem(&service->listeners, l) {
		if (l->io == NULL && l->fd != -1)
			l->io = io_add(l->fd, IO_READ, service_accept, l);
	}
}

void service_monitor_listen_start(struct service *service)
{
	if (service->process_avail > 0 || service->to_throttle != NULL ||
	    (service->process_count == service->process_limit &&
	     service->listen_pending))
		return;

	service_monitor_listen_start_force(service);
}

void service_monitor_listen_stop(struct service *service)
{
	struct service_listener *l;

	array_foreach_elem(&service->listeners, l)
		io_remove(&l->io);
	service->listening = FALSE;
	service->listen_pending = FALSE;
	timeout_remove(&service->to_drop);
	timeout_remove(&service->to_drop_warning);
}

static int service_login_create_notify_fd(struct service *service)
{
	int fd, ret;

	if (service->login_notify_fd != -1)
		return 0;

	T_BEGIN {
		string_t *prefix = t_str_new(128);
		const char *path;

		str_append(prefix, service->list->set->base_dir);
		str_append(prefix, "/login-master-notify");

		fd = safe_mkstemp(prefix, 0600, (uid_t)-1, (gid_t)-1);
		path = str_c(prefix);

		if (fd == -1) {
			e_error(service->event, "safe_mkstemp(%s) failed: %m",
				      path);
		} else if (unlink(path) < 0) {
			e_error(service->event, "unlink(%s) failed: %m", path);
		} else {
			fd_close_on_exec(fd, TRUE);
			service->login_notify_fd = fd;
		}
	} T_END;

	ret = fd == -1 ? -1 : 0;
	if (fd != service->login_notify_fd)
		i_close_fd(&fd);
	return ret;
}

void services_monitor_start(struct service_list *service_list)
{
	ARRAY(struct service *) listener_services;
	struct service *service;

	if (services_log_init(service_list) < 0)
		return;
	service_anvil_monitor_start(service_list);

	if (service_list->io_master == NULL &&
	    service_list->master_fd != -1) {
		service_list->io_master =
			io_add(service_list->master_fd, IO_READ,
			       master_client_connected, service_list);
	}

	t_array_init(&listener_services, array_count(&service_list->services));
	array_foreach_elem(&service_list->services, service) {
		if (service->type == SERVICE_TYPE_LOGIN) {
			if (service_login_create_notify_fd(service) < 0)
				continue;
		}
		if (service->master_dead_pipe_fd[0] == -1) {
			if (pipe(service->master_dead_pipe_fd) < 0) {
				e_error(service->event, "pipe() failed: %m");
				continue;
			}
			fd_close_on_exec(service->master_dead_pipe_fd[0], TRUE);
			fd_close_on_exec(service->master_dead_pipe_fd[1], TRUE);
		}
		if (service->status_fd[0] == -1) {
			/* we haven't yet created status pipe */
			if (pipe(service->status_fd) < 0) {
				e_error(service->event, "pipe() failed: %m");
				continue;
			}

			net_set_nonblock(service->status_fd[0], TRUE);
			fd_close_on_exec(service->status_fd[0], TRUE);
			net_set_nonblock(service->status_fd[1], TRUE);
			fd_close_on_exec(service->status_fd[1], TRUE);
		}
		if (service->io_status == NULL) {
			service->io_status =
				io_add(service->status_fd[0], IO_READ,
				       service_status_input, service);
		}
		service_monitor_listen_start(service);
		array_push_back(&listener_services, &service);
	}

	/* create processes only after adding all listeners */
	array_foreach_elem(&listener_services, service)
		service_monitor_start_extra_avail(service);

	if (service_list->log->status_fd[0] != -1) {
		if (service_process_create(service_list->log) != NULL)
			service_monitor_listen_stop(service_list->log);
	}

	/* start up a process for startup-services */
	array_foreach_elem(&service_list->services, service) {
		if (service->type == SERVICE_TYPE_STARTUP &&
		    service->status_fd[0] != -1) {
			if (service_process_create(service) != NULL)
				service_monitor_listen_stop(service);
		}
	}
}

static void service_monitor_close_dead_pipe(struct service *service)
{
	if (service->master_dead_pipe_fd[0] != -1) {
		i_close_fd(&service->master_dead_pipe_fd[0]);
		i_close_fd(&service->master_dead_pipe_fd[1]);
	}
}

void service_monitor_stop(struct service *service)
{
	int i;

	io_remove(&service->io_status);

	if (service->status_fd[0] != -1 &&
	    service->type != SERVICE_TYPE_ANVIL) {
		for (i = 0; i < 2; i++) {
			if (close(service->status_fd[i]) < 0) {
				e_error(service->event,
					      "close(status fd) failed: %m");
			}
			service->status_fd[i] = -1;
		}
	}
	service_monitor_close_dead_pipe(service);
	if (service->login_notify_fd != -1) {
		if (close(service->login_notify_fd) < 0) {
			e_error(service->event,
				      "close(login notify fd) failed: %m");
		}
		service->login_notify_fd = -1;
	}
	timeout_remove(&service->to_login_notify);
	service_monitor_listen_stop(service);

	timeout_remove(&service->to_throttle);
	timeout_remove(&service->to_prefork);
	timeout_remove(&service->to_idle);
}

void service_monitor_stop_close(struct service *service)
{
	struct service_listener *l;

	service_monitor_stop(service);

	array_foreach_elem(&service->listeners, l)
		i_close_fd(&l->fd);
}

static void services_monitor_wait(struct service_list *service_list)
{
	struct service *service;
	struct timeval tv_start;
	bool finished;

	io_loop_time_refresh();
	tv_start = ioloop_timeval;

	for (;;) {
		finished = TRUE;
		services_monitor_reap_children();
		array_foreach_elem(&service_list->services, service) {
			if (service->status_fd[0] != -1)
				service_status_input(service);
			if (service->process_avail > 0)
				finished = FALSE;
		}
		io_loop_time_refresh();
		if (finished ||
		    timeval_diff_msecs(&ioloop_timeval, &tv_start) > MAX_DIE_WAIT_MSECS)
			break;
		i_sleep_msecs(10);
	}
}

static bool
service_processes_list_close_listeners(struct service *service,
				       struct service_process *processes)
{
	struct service_process *process = processes;
	bool ret = FALSE;

	for (; process != NULL; process = process->next) {
		if (kill(process->pid, SIGQUIT) == 0)
			ret = TRUE;
		else if (errno != ESRCH) {
			e_error(service->event, "kill(%s, SIGQUIT) failed: %m",
				      dec2str(process->pid));
		}
	}
	return ret;
}

static bool service_processes_close_listeners(struct service *service)
{
	bool ret = FALSE;

	if (service_processes_list_close_listeners(service,
						   service->busy_processes))
		ret = TRUE;
	if (service_processes_list_close_listeners(service,
						   service->idle_processes_head))
		ret = TRUE;
	return ret;
}

static bool
service_list_processes_close_listeners(struct service_list *service_list)
{
	struct service *service;
	bool ret = FALSE;

	array_foreach_elem(&service_list->services, service) {
		if (service_processes_close_listeners(service)) {
			if (service->type != SERVICE_TYPE_LOG)
				ret = TRUE;
			else {
				/* The log process won't stop until we close its
				   fds later on. Send a SIGQUIT to it anyway
				   just in case it's stuck for some reason, but
				   don't wait for it to be processed. This way
				   there is no unnecessary 1sec wait. */
			}
		}
	}
	return ret;
}

static void services_monitor_wait_and_kill(struct service_list *service_list)
{
	/* we've notified all children that the master is dead.
	   now wait for the children to either die or to tell that
	   they're no longer listening for new connections. */
	services_monitor_wait(service_list);

	/* Even if the waiting stopped early because all the process_avail==0,
	   it can mean that there are processes that have the listener socket
	   open (just not actively being listened to). We'll need to make sure
	   that those sockets are closed before we exit, so that a restart
	   won't fail. Do this by sending SIGQUIT to all the child processes
	   that are left, which are handled by lib-master to immediately close
	   the listener in the signal handler itself. */
	if (service_list_processes_close_listeners(service_list)) {
		/* SIGQUITs were sent. wait a little bit to make sure they're
		   also processed before quitting. */
		i_sleep_msecs(1000);
	}
}

void services_monitor_stop(struct service_list *service_list, bool wait)
{
	struct service *service;

	array_foreach_elem(&service_list->services, service)
		service_monitor_close_dead_pipe(service);

	if (wait)
		services_monitor_wait_and_kill(service_list);

	io_remove(&service_list->io_master);

	array_foreach_elem(&service_list->services, service)
		service_monitor_stop(service);

	services_log_deinit(service_list);
}

static bool
service_has_successful_processes_in_list(struct service *service,
					 struct service_process *processes)
{
	/* See if there is a process that has existed for a while and has
	   received the initial status notification. The oldest processes are
	   last in the list, so just scan through all of them. */
	struct service_process *process = processes;
	for (; process != NULL; process = process->next) {
		time_t age_secs = ioloop_time - process->create_time;
		if (age_secs >= SERVICE_MIN_SUCCESSFUL_AGE_SECS &&
		    process->to_status == NULL) {
			/* Remember this so this list doesn't have to be
			   scanned again. */
			service->have_successful_exits = TRUE;
			return TRUE;
		}
	}
	return FALSE;
}

static bool service_has_successful_processes(struct service *service)
{
	if (service->have_successful_exits)
		return TRUE;

	return service_has_successful_processes_in_list(service,
			service->busy_processes) ||
		service_has_successful_processes_in_list(service,
			service->idle_processes_head);
}

static bool
service_process_failure(struct service_process *process, int status)
{
	struct service *service = process->service;
	bool throttle;

	service_process_log_status_error(process, status);
	throttle = process->to_status != NULL;
	if (!throttle && !service_has_successful_processes(service)) {
		/* This service has seen no successful exits yet and no
		   processes that were already running for a while.
		   Try to avoid failure storms at Dovecot startup by throttling
		   the service if it only keeps failing rapidly. This is no
		   longer done after the service looks to be generally working,
		   in case an attacker finds a way to quickly crash their own
		   session. */
		if (service->exit_failure_last != ioloop_time) {
			service->exit_failure_last = ioloop_time;
			service->exit_failures_in_sec = 0;
		}
		if (++service->exit_failures_in_sec > SERVICE_MAX_EXIT_FAILURES_IN_SEC)
			throttle = TRUE;
	}
	service_process_notify_add(service_anvil_global->kills, process);
	return throttle;
}

void services_monitor_reap_children(void)
{
	struct service_process *process;
	struct service *service;
	pid_t pid;
	int status;
	bool service_stopped, throttle;

	while ((pid = waitpid(-1, &status, WNOHANG)) > 0) {
		process = hash_table_lookup(service_pids, POINTER_CAST(pid));
		if (process == NULL) {
			i_error("waitpid() returned unknown PID %s",
				dec2str(pid));
			continue;
		}

		service = process->service;
		if (status == 0) {
			/* success - one success resets all failures */
			service->have_successful_exits = TRUE;
			service->exit_failures_in_sec = 0;
			service->throttle_msecs =
				SERVICE_STARTUP_FAILURE_THROTTLE_MIN_MSECS;
			throttle = FALSE;
		} else {
			throttle = service_process_failure(process, status);
		}
		if (service->type == SERVICE_TYPE_ANVIL)
			service_anvil_process_destroyed(process);

		/* if we're reloading, we may get here with a service list
		   that's going to be destroyed after this process is
		   destroyed. keep the list referenced until we're done. */
		service_list_ref(service->list);
		service_process_destroy(process);

		if (throttle)
			service_monitor_throttle(service);
		service_stopped = service->status_fd[0] == -1;
		if (!service_stopped && !service->list->destroying) {
			service_monitor_start_extra_avail(service);
			/* if there are no longer listening processes,
			   start listening for more */
			if (service->to_throttle != NULL) {
				/* throttling */
			} else if (service == service->list->log &&
				   service->process_count == 0) {
				/* log service must always be running */
				if (service_process_create(service) == NULL)
					service_monitor_throttle(service);
			} else {
				service_monitor_listen_start(service);
			}
		}
		service_list_unref(service->list);
	}
}
